"I will say it openly: Poland has gained such significant influence in foreign policy, that the so-called high representative would be within the scope of our interests," Tusk told reporters. "Radoslaw Sikorski would be a natural candidate."

The role, officially the High Representative for Foreign Affairs and Security Policy, is seen as that of the EU's "foreign minister".Ashton has held the post for five years, but has ruled out standing for a second term.

Sikorski, 51, has been foreign minister since 2007, and for two years before that was defense minister.

He was a leading figure in the international diplomatic response to the Ukraine crisis earlier this year.

The European Council will vote on the appointment in July, but MEPs will have to confirm the appointment in September.